Squirrel-cage induction motors only have one moving part, the rotor, and no semiconductors, and they can have quite a bit of clearance around the rotor, especially if efficiency isn't important. You might need to grease the bearings, and if they're rolling-element bearings, they'll wear out eventually and need to be replaced; but bearing wear is proportional to the loads on the shaft that the bearing has to resist. In a low-powered fan, a plain bearing or a reasonably sized ball bearing ought to have both MTBF and wearout time well into the decades if not centuries.
That's how it's possible. It's not even difficult. Unless you buy the fan on Amazon.